If you concede the actual in game decisions, such as lineup order, when to yank a pitcher, who to move in and out of lineup, bullpen choices, etc are minimal just because most guys would make the same decisions. So one could argue they only matter for a small amount of games per year difference. I'm not saying that's the case, but just say you did. But I'd add one of the biggest factors a manager has is on locker room morale/culture, everyone having a positive attitude team first attitude. I guess similar to a good boss in normal world. Managers are crucial to this and it sure seems Counsel has been one of the best at it for his tenure. Though I'd grant this year doesn't seem to be as good on that front, for whatever reason.
Just watching some White Sox stuff today. Thinking of their talent, and how weak their division is, it's hard to think a different manager wouldn't have won that division. Flip Francona and LaRussa and I bet that flips the division.